Black Holes
A black hole is a mass that has collapsed in on itself under its own gravitational power. The mass required to collapse into a black hole is about 2 solar masses. While some people suspect that there are black holes in their dryers that suck up half pairs of socks the fact is that a black hole with an event horizon large enough to swallow a sock would have a mass greater than the earth. Since the planet does not revolve around washers and dryers there is just one enevitable conclusion... all the washers and dryers are arranged spherically around the globe so that their gravitational influence exactly cancel each other out.
A journey into a black hole begins at the event horizon. The event horizon is so called because the event at the end of every possible trajectory inside it ends up at the center of the black hole. Unlike popular artistic representations of black holes the event horizon does not look like a definite sphere. Rather light rays just outside of the event horizon can excape the black holes pull only if they are going nearly straight away from the horizon. The farther away from the event horizon a light beam is the closer to tangent to the event horizon a light beam can be and still escape. Annother way of visualizing this is in terms of cones. Imagine a flat plane a distance away from the sphere of a black hole equal to twice the diameter of the sphere. At this distance all light beams heading away from the event horizon or even that are parralell to it will never cross it. As we move the plane towards the black hole we find that it turns into a cone a very shallow one at first and then more and more pointed as we approach the hole. When the distance to the event horizon is zero the cone has devolved into a single line meaning that only light beams traveling exactly out from the event horizon can avoid being sucked into the black hole. Photons that are emitted at the event horizon exactly normal to the event horizon are frozen at the horizon making a sort of light shell surrounding the hole. Once inside the black hole nothing can escape being drawn enevitably to the center or the singularity. Before we talk about what the singularity we should make a note about the behavior of the space inbetween the event horizon and the singularity itself. Physicists find that inside a black hole the equations of relativity suggest that space might become timelike and time spacelike. This is true in the sense that space has become uni-directional because all paths through space lead "forward" towards the singularity just as all paths in time seem to move forward to the future. Time inside a black hole is said to possibly become spacelike and permit time travel because time is usually assosicated with an imaginary number and inside a black hole when the equations are solved the time variable may well become a real number like the ordinary space dimensions. A time traveler hoping to utilize a black hole to travel through time would not want to stray too close to the singularity or they would be destroyed so their only hope lies in the space between. Traveling all the way down to the strange world of the singularity we find a great deal of strangeness indeed. The Singularity is a place of which we can be sure of very little. we cannot even be certain of what happens just inside the event horizon since we cannot hope to observe the inside of a black hole as there would be no way to send a message from the inside of the hole to the outside. However based on the implications of our current physical theories the curvature of spacetime immediately around the singularity is infinite. The infinite curvature of the space around the singularity translates to infinite forces that crush all matter to a single point. We treat the singularity in a black hole as a zero dimensional object even though we have no way of knowing if this is truly accurate since our laws of physics completely break down very close to the singularity and become meaningless. physicists have espoused the notion that quantum effects make it impossible for the black hole to have a density greater than 1094 grams/cm which would eliminate a great deal of the problems by limiting the mass of a black hole to the plank density which is the boundary beyond which regular physics is garanteed to begin misbehaving because of inconsistiencies between relativity and quantum mechanics. This truncation of the physical world seems arbitrary to many and seems to be a simple patch job that gives workable results without needing a good unified theory of quantum gravity. A better solution would be a renormalizable four dimensional gauge theory for quantum gravity... but that is easier said than done and it isn't even that easy to say. The event horizon for a non rotating black hole has a dimension directly proportional to its mass. The schwartzchild radius is about equal to GM/C2 where G is the gravitational constant M is the mass in kilograms and C is the speed of light. The schwartzchild radius is not to be taken litteraly since the space inside the event horizon gets infinitely curved the radius of any black hole would actually be infinite but the schwartzchild radius is meant to describe a sphere on a superimposed euclidean space. The space immediately around the event horizon is subject to tidal gravitational forces meaning that the gravitational attraction on one side of a body is greater than the attraction on the other like the effect of the moon on the earth which causes tides on both sides of the earth on one side because of the gravitational attraction of teh moon and on the other because of the weakened gravitational attraction of the moon but the same accelerational forces caused by the earth and moon's rotation around each other. In the case of a black hole the tidal gravitational forces can be so strong that they rip virtual particle antiparticle pairs appart making one of the two particles real. The smaller the black hole the greater the tidal forces and so the more particles which can be created by the virtual particle flux around a black hole. But better yet than the fact that the event horizon of a black hole has a temperature is the fact that the space around the event horizon actually has a negative energy density.
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